Melanophores
These cells synthesize and contain black and brown pigmentation known as melanin. There are two kinds of melanophores present, dermal and epidermal. Dermal melanophores are located in the upper dermis, while epidermal melanophores are located in the lower epidermis skin layers.
The process of creating melanin is fairly simple. Tyrosine, which is a type of amino acid, is converted into dopa, and then into dopaquinone in the presence of tyrosinase, which is synthesized by the melanophores. Dopaquinone is later modified into melanin and deposited in the appropriate melanophores. This is the root of the terms 'Tyrosinase-positive (T+)' and 'Tyrosinase negative (T-)' albinos.
In T- albinos, tyrosinase is not produced by the melanophores and no melanin is ever created in the melanophores. The result is an animal possessing absolutely no black or dark brown pigment whatsoever.
In the T+ form of albino, tyrosinase is produced but is blocked from gaining access into the melanophores. Simply put, all the parts are there - they just can't mix. However, in most specimens there is a certain amount of 'mixing' that occurs by cells disrupting or possibly by osmotic transfer. The exact method is unclear, and may vary. What is clear is that T+ albinos are generally darker than their counterparts, often containing traces of melanin deposits that result in a slightly darker look than the T- albinos of the same specie. Often red coloration is particularly prominent and many times the eyes are dramatically darker than expected.
Xanthophores
These chromatophores produce red and yellow pigments known as pteridines. These may vary in color from pure yellow to pure red, as well as intermediate shades. Xanthophores possessing a predominantly red coloration are referred to as erythrophores.'
The Learning Center - Chromatophores